It is an instrument used to measure the relative humidity of the atmosphere.
It consists of a thermometer with a bulb that is wet or moist and one that is kept dry. The relative humidity is calculated from the difference in readings of the thermometers when water evaporates from the wet bulb, decreasing its temperature.
Identical dry and wet bulb temperatures mean that there is 100% relative humidity.
Our device consists of two thermometers fitted on a scale, with readings both in Centigrade and Fahrenheit.
The temperature range is from -15 to +120 x 2°F and -10 to +50 x 1°C.
Red alcohol is filled for easy readability.
One thermometer bulb is covered with muslin, which is kept moist by being connected to a reservoir of water. This wet bulb thermometer measures the latent heat content of the moisture-laden air.
The other thermometer has the bulb exposed and dry for the dry-bulb temperature. It measures the sensible air temperature.
The entire set up is mounted on a plastic base and it can be mounted on a wall.
The apparatus is supplied with a humidity and temperature conversion chart.